1. Field of the Invention
The present invention relates to a light-emitting diode driver, and more particularly, a light-emitting diode driver having a logic unit for generating a frequency control signal.
2. Description of the Prior Art
When adjusting backlight brightness of a liquid crystal display of the prior art, a user instruction, an image data and ambient light are analyzed to generate a brightness signal, and the brightness signal is sent to a light-emitting display (LED) driver for adjusting the backlight. Techniques such as Sunlight Readability Enhancement (SRE) may be used for analyzing ambient light to increase the display brightness when detecting brighter ambient light. Techniques such as Content Adaptive Brightness Control (CABC) may be used for analyzing an image data for optimizing the display brightness and contrast according to the displayed image. Either a pulse-frequency modulation (PFM) technique or a pulse-width modulation (PWM) technique may be adopted for controlling the display brightness. When using the pulse-frequency modulation technique, a duty cycle of a control signal controlling a switch of the light-emitting display driver is fixed, and a frequency of the control signal is adjustable. When using the pulse-width modulation technique, the duty cycle of the control signal is adjustable, and the frequency of the control signal is fixed. The pulse-frequency modulation technique usually leads to lower efficiency when driving a heavy load, poor performance of noise reduction and median level of output ripples, and merely has an advantage of good efficiency when driving a light load. The pulse-width modulation technique usually leads to good efficiency for driving a heavy load, ideal performance of noise reduction and output ripples being small enough, but the pulse-width modulation technique has poor efficiency for driving a light load. Hence, a solution for a light-emitting display driver to have good performance of driving a heavy load and a light load, reduce noise greatly and output small ripples is required in the field.